1. Field of the Invention
The present invention relates to a method for fabricating an envelope for maintaining a vacuum interior, and a method for fabricating an image display apparatus utilizing the method for fabricating the envelope.
2. Related Background Art
An electron emitting device has been known in two types of a hot electron source and a cold cathode electron source. The cold cathode electron source includes an electric field emission device (FE device), a metal/insulator/metal device (MIM device), a surface conduction electron emitting device (SCE device) etc.
FIG. 12 schematically shows an envelope 91 utilizing an electron source substrate, in which such electron emitting devices (an surface conduction electron emitting device being shown as an example) are arranged in a matrix shape. A rear plate 93 is a glass substrate provided, on one side thereof, with an electron source substrate 131 on which a plurality of surface conduction electron emitting devices 132 are arranged. The electron emitting device 132 is provided with a pair of device electrodes, which are respectively connected to an X-direction wiring 133 and a Y-direction wiring 134. A face plate 92 is formed by a glass substrate 121, bearing, on an internal surface thereof, a fluorescent film 122, a metal back 123 etc. Between the face plate 92 and the rear plate 93, a supporting frame 94 is provided to secure a predetermined space between the electron emitting device 132 and the fluorescent film 122/metal back 123. A getter (not shown) of an evaporation type or a non-evaporation type is provided on an image display area of the face plate 92, or the electron source substrate 131 of the rear plate 93, or on both glass substrates. Between the face plate 92 and the rear plate 93, a support member (not shown) called a spacer may be further provided. Presence of such spacer allows to form an envelope 91 having a sufficient strength to the atmospheric pressure even in case of a large-area panel.
FIG. 13A shows an example of a procedure of fabricating the envelope (for example cf. Japanese Patent Application Laid-open No. H11-135018). For forming the envelope 91, at first a face plate 92 and a rear plate 93 are prepared (step 101). In this state, a support frame 94 is adhered in advance to the face plate 92 by frit glass, and, in case of employing a spacer, such spacer is adhered and fixed to the rear plate 93. Then, as a panel adjoining material, an In film (not shown) is coated by soldering on the support frame 94 and the rear plate 93 (step 102). In order to improve the adhesion strength of the support frame 94 and the rear plate 94 to the In film, a silver paste film may be provided as an undercoat layer (not shown). Also a sufficient adjoining strength can be obtained by a soldering with an ultrasonic soldering iron. Then the face plate 92 and the rear plate 93 are carried to a sealing apparatus, and are subjected to a vacuum baking (step 103). Then a getter activation process is executed under vacuum (step 104), and then the support frame 94 and the rear plate 93 are adjoined and sealed across the In film at a temperature equal to or higher than the melting point of In, thereby completing an envelope 91 (step 105).
However, the vacuum baking step and the sealing step executed in a same chamber result in a drawback of an elongated process time required for temperature regulation and the like. Therefore, an improvement in the fabrication efficiency is achieved by executing these steps in different chambers. FIG. 13B shows an example of such fabricating process. Steps 111 and 112 and same as the aforementioned steps 101 and 102. After a vacuum baking step (step 113), the face plate 92 and the rear plate 93 are carried to a sealing apparatus capable of executing the getter process (step 114), in which a getter step and a sealing step are executed (steps 115, 116). In this process, in order that the face plate 92 and the rear plate 93 subjected to a dehydration and a degassing in the vacuum baking step are not recontaminated by an impurity or water in the course of carrying, thereby resulting in a loss of vacuum level, the carrying is executed in vacuum or in an inert gas atmosphere such as a N2 atmosphere.
However, such prior process is associated with following drawbacks. Firstly, the In coating step cannot be executed effectively in vacuum because of In scattering, and has to be executed prior to the baking step because the steps of baking and thereafter are all executed in vacuum in the prior technology, so that the process lacks freedom.
Also the spacer provided on the rear plate is heated to a high temperature by vacuum baking, and a rapid temperature change induces a bending of the rear plate and a cracking of the spacer. Thus, there are required measures against the cracking of the spacer, such as a temperature control by upper and lower heaters at the carrying operation, involving a difficulty in the temperature control and an increased cost of the apparatus. On the other hand, a carrying in an inert gas atmosphere also requires measures for preventing oxygen deficiency or choking around the carrying facility, resulting in a difficult process control and an increase in the facility cost.